Well depending on the barrel quality & bullet, a barrel can copper foul out by ~some number of shots.
And if you're leaving petroleum products in the bore -it has to be burned out before establishing stable fouling.
I have actually seen a barrel that would copper foul out by 10shts.. I had to fire lap that bore with Tubb's FF before proceeding with any development.
For ladder testing you only need 30 good shots. But beforehand, shoot a 5sht group, just to prefoul a cleaned bore.
If that's inline with your cleaning plan & field use, then clean after the ladder session, and do the same when your ready for group shooting (incremental load development).
If you plan to go 50shts before cleanings, do that. See if it will -before groups open from copper.
If you want to to go 100shts between, then in my experience you'll have to do more than just choose it. You can go to a dry pre-fouling plan and get a lot more GOOD shots between cleanings.